A number of detector structures are available for use in ion-implanted contiguous-disk bubble devices. In IBM Technical Disclosure Bulletin, Vol. 22, No. 4, page 1704 September 1979, A Two-way Stretcher for Contiguous-Disk Sensors is described. This detection system however, uses the self-aligned approach, that is, it uses the control conductor as an implantation mask and requires high current applitudes for bubble expansion of the order of 200 mA or more. This causes large power dissipation which limits the usefulness of the device, particularly at high frequency of operations, say 200 kHz or greater. In IBM Technical Disclosure Bulletin Vol. 24 No. 5, page 2398, October 1981, A Center Fed Ion-Implanted Channel High Speed Bubble Detector for Contiguous-Disk Devices is described. This detector consists of a hairpin conductor positioned on a narrow ion-implanted channel. The detector, however, suffers from erratic nucleation of bubble domains in the ion-implanted channel.
Bubble detectors for ion-implanted devices are also described in the Bell System Technical Journal, Vol. 59 No. 2, page 229 February 1980. These detectors expand bubbles in one direction only and employ either a hairpin conductor positioned over an ion-implanted channel or a hairpin conductor positioned over a totally implanted or a totally non-implanted region. These detectors exhibit relatively poor operating margins and cannot be used at high operating frequencies because of the time limitation imposed by unidirectional expansion. In general they are suitable for frequencies of no more than 50 kHz.
Another bubble detector is described in Journal of Applied Physics, Vol. 53 No. 3, page 2525, March 1982. This is a non-destructive detector, that is, one in which the bubble domain is preserved after detection. It provides unidirectional bubble expansion using two sets of control conductors positioned over a totally non-implanted area. The frequency of operation is 50 kHz.